U.S. Pat. No. 1,904,573 to Tuley relates to the treatment of natural rubber in the presence of an organic accelerator. More specifically Tuley relates to a substantial reduction in compounding cost by reducing the customary amounts of organic accelerators and using in supplantation thereof inexpensive and substantially neutral acid amides such as urea.
U.S. Pat. No. 2,812,373 to Zerbe relates to apparently unreacted mixtures of urea and various compounds such as carboxylic acids, straight-chain paraffins, mercaptans, and alkyl amines to yield an adduct of urea which acts as an activator capable of assisting primary organic vulcanization accelerators.